The present invention relates to a post-processing device that is installed in a paper processing apparatus having a paper processing section applying a predetermined process to paper and that performs a post-processing for the paper that has undergone the predetermined process in the paper processing section, and to a paper processing apparatus provided with the post-processing device.
Among some paper processing apparatus such as image forming apparatus are those provided with a post-processing device configured so as to perform a binding process such as stapling process, a perforation process and an offset process.
The post-processing device typically includes an introductory conveying path conveying paper introduced from the paper processing section such as image forming section, a processing tray onto which the paper having passed through the introductory conveying path is placed, and a paper receiving tray onto which the paper is discharged from the processing tray after having undergone a post-processing on the processing tray (for example, refer to Japanese Patent Unexamined Publication No. 2006-248685 bulletin).
In such a post-processing device, as shown in FIG. 1A through FIG. 1C, most part of a paper sheet 80 is typically once placed onto the paper receiving tray 28 with an upper paper discharge roller 229 and a lower paper discharge roller 244 disposed in a state of being away from each other, until the rear end portion of the paper sheet 80 reaches between the upper paper discharge roller 229 and the lower paper discharge roller 244 when the paper sheet 80 to be post-processed passes through the introductory conveying path 222. Thereafter, when the rear end portion of the paper sheet 80 has reached between the upper paper discharge roller 229 and the lower paper discharge roller 244, the paper sheet 80 is drawn into the processing tray 24 by the upper paper discharge roller 229 and the lower paper discharge roller 244 rotating together while the upper paper discharge roller 229 contacts with the lower paper discharge roller 244 with pressure. On the processing tray 24, it is necessary for the paper sheets 80 to be placed at a predetermined alignment position in order that the paper sheets 80 are accurately post-processed.
In conventional post-processing devices, however, if the paper sheet 80 is of relatively light weight such as thin paper, small-sized paper and/or the like, variation in the distribution of the paper sheets 80 increases that are conveyed from the introductory conveying path 222 to the paper receiving tray 28, as shown in FIG. 2A and FIG. 2B. The reason being that after passing through the introductory conveying path 222 the paper sheet 80 is never gripped by any pairs of rollers until it is gripped at its rear end portion by the upper paper discharge roller 229 and the lower paper discharge roller 244. To put it concretely, when the paper sheet 80 is conveyed from the introductory conveying path 222 to the paper receiving tray 28, and if the paper sheet 80 is relatively heavy, the paper sheet 80 is placed at a generally fixed position on the paper receiving tray 28 by its own weight. On the other hand, if the paper sheet 80 is of relatively lightweight, the paper sheets 80 are likely to be scattered on the paper receiving tray 28 by the impetus at the time when they are each discharged from the introductory conveying path 222, and in particular, ways of sliding and bouncing of the paper sheets 80 after the leading edge of the paper sheets 80 have each collided against the paper receiving tray 28 are varied, thereby increasing the variation in the distribution of the paper sheets 80 on the paper receiving tray 28. If the variation in the distribution of the paper sheets 80 is large on the paper receiving tray 28, alignment of the paper sheets 80 drawn onto the processing tray 24 becomes untidy, resulting in a problem that accuracy in performing the post-processing of the paper sheet(s) 80 deteriorates.
The present invention is directed to providing a post-processing device capable of increasing the alignment of paper on a processing tray by controlling a variation in the distribution of paper conveyed from an introductory conveying path to a paper receiving tray, and a paper processing apparatus provided with the post-processing device.